This verse expresses in a negative form the thought of the previous verse; the negative statement following the positive statement is a form of emphasis. This same technique was followed in verse 3.

He himself (so also New English Bible, New American Bible; “he” of Revised Standard Version, Moffatt, Goodspeed, Jerusalem Bible; “that man” of Phillips) is literally “that one.” The second clause of this verse contains no verb, but most translations supply the verb came (Phillips “was sent”). The Die Bibel im heutigen Deutsch restructures completely: “his task was only to point to the Light”

In some languages it may not make sense to say He himself was not the light, since this could be interpreted as saying “John was not a torch”—an obvious truth. Therefore, it may be necessary to render this clause “He himself was not the one who brought light to mankind.”

Because of the contrast between the negative and positive statements, it may be important to emphasize this distinction by translating the second clause of verse 8 “he came just to tell about that light.”

Quoted with permission from Newman, Barclay M. and Nida, Eugene A. A Handbook on the Gospel of John. (UBS Handbook Series). New York: UBS, 1980. For this and other handbooks for translators see here .